New species of chitons of the superfamily Cryptoplacoidea (Mollusca: Polyplacophora) from Vietnamese waters Author Sirenko, Boris I. Author Saito, Hiroshi text Zootaxa 2017 4299 4 451 506 journal article 32590 10.11646/zootaxa.4299.4.1 e9fcac10-f2bf-4f24-b015-b8c0f18faa14 1175-5326 836971 DEB133FB-9D5A-4F17-A718-568ACA9BA9D7 Genus Leptoplax (Carpenter MS) Dall, 1882 Type species. Chiton coarctatus Sowerby, 1841 , by monotypy. Diagnosis. Medium chitons. Tegmentum rather wide to reduced, with well defined, narrow to wedge-shaped jugum; lateral and pleural areas hardly separable (occasionally separable with larger pustules on diagonal line). Articulamentum large; sutural laminae concave in antero-lateral edge in tail valve; insertion plates medium to large on all valves; slit formula 5/1/3-10. Girdle large, thick, fleshy, densely spiculose, usually not completely encroaching between valves; sutural tufts always present, but usually not prominent. Radula teeth arranged symmetrically (rarely asymmetrical in central part); central tooth asymmetrical, spatula-shaped or those with wide basal portion, concave in the distal half, keeled at base; first lateral (centro-lateral) tooth of radula with thin or slightly thickened antero-dorsal corner; median denticle of tricuspid major lateral tooth long, but not as long as in Notoplax (radula characters: after Saito, 2004 with modification). FIGURE 7. Notoplax odysseyi n. sp. , Southern Vietnam, Off Phan Rang, holotype, BL 51 mm: A. Pustules on the front edge of valve IV; B. Needles of tuft; C. Dorsal needles; D. Radula. Remarks. The genus Leptoplax had been considered to represent a synonym of the genus Notoplax but has been reinstated by Gowlett-Holmes (2001) after redefinition of the latter genus ( Gowlett-Holmes 1991 ), although the redefinition of Leptoplax has not been given to date. Here we propose a new definition. The main criteria to distinguish the two genera are the morphology of the sutural laminae of the tail valve and the radula, especially of the central and the first lateral teeth. However, further research including molecular analysis is needed to establish better definition for both genera.